For some time many flowable liquid and flowable solid products have been packaged in thermoplastic packaging films, such a polyethylene, polypropylene, etc, using vertical-form-fill-and-seal packaging equipment. The packaging of explosive compositions, such as ammonium nitrate, has used vertical-form-fill-and-seal equipment, in which the explosive ammonium nitrate composition has the viscosity of a soft putty, and hence is flowable.
In the past, vertical-form-fill-and-seal packaging of ammonium nitrate has utilized a high strength flexible film packaging material marketed by Van Leer Flexibles, Inc. of Houston, Tex., i.e., VALERON.RTM. strength film. VALERON.RTM. strength film is made from high density oriented and cross-laminated polyethylene, and is stated as being puncture-resistant, tear-resistant, and chemical-resistant. VALERON.RTM. strength film is also stated as being strong, with a smooth surface, balanced tear-resistance, of uniform thickness, and is printable with solvent-based and water-based inks, and is laminatable to paper, film, and other substrates. VALERON.RTM. strength film is also stated as maintaining its properties in harsh environments and as having a temperature operating range of from -70.degree. F. to over 200.degree. F., and as being useful in the flexible packaging, shipping, construction, agricultural, photographic, and tag & label industries. VALERON.RTM. strength film is stated as having much better tear-resistance than single-ply film of the same overall thickness and of the same polymer which has been biaxially oriented. VALERON.RTM. strength film has also been stated to provide improvements over even other cross-laminated films because it is annealed, i.e., subjected to an elevated temperature (i.e., from 35.degree. C. to below the lowest melting point of the thermoplastic material present, excluding any adhesive or bonding layer). The annealing process reportedly provides VALERON.RTM. strength film with a higher impact strength relative to corresponding unannealed films.
In the packaging of explosive products in VALERON.RTM. strength film using vertical-form-fill-and-seal equipment, at least one bead, and preferably two beads, of a molten thermoplastic material, such as polyethylene homopolymer or copolymer, especially ethylene/vinyl acetate copolymer, or NOVACOR.RTM. SC7250 SCLAIRCOAT polyethylene, obtained from Nova Chemical, of Alberta, Canada, have been used in order to form a lap seal along the length of the resulting package, which contains a "chub" of the explosive product. It is important that the resulting package does not burst when dropped onto a hard surface (or water) from a distance of from 10 to 50 or more feet. The use of the molten plastic adhesive is apparently needed to ensure adequate seal strength and adequate water resistance. If the film bursts, the explosive composition could be exposed to water or other contamination which impairs its ability to explode.
Thus, it is necessary to provide a packaging film for explosives which can be sealed using vertical form fill and seal equipment, so that the resulting packaging material, when sealed around the explosive article, does not burst when it is dropped onto a hard surface (or water) from a significant height. Although VALERON.RTM. strength film has been used for this purpose, is a relatively expensive product, i.e., compared with other packaging films. This expense is undoubtedly associated with the costs of cross-laminating and annealing. It would be desirable to provide high strength, flexible film packaging which can be sealed using vertical form fill and seal packaging equipment in a manner which yields performance characteristics comparable to VALERON.RTM. strength film, but which is less complex to manufacture.